Electroless or autocatalytic or chemical coating of dielectric (non-conductor) substrates or composite printed circuitry substrates are well known processes finding wide utility in the preparation of such diverse articles as printed circuitry arrays (e.g., PTH), automotive trim, decorative plating, mirrors, decorative silver spray and the like. Normal electroless coating processes generally involve an initial cleaning and/or etching of the substrate by physical or chemical means as to improve the adherence of the metallic coating. In addition, the etched substrate generally provides with improved wettability toward water. The etched surface is then catalyzed or sensitized by suitable catalytic composition and processes to provide a surface capable of electroless (chemical) plating initiation.
In the prior art the catalytic treatment generally encompassed the use of precious metals (e.g., palladium). More recently, compositions and processes utilizing non-precious metals have been disclosed suitable for electroless plating of dielectrics. The following U.S. patents disclose the prior art as applied to non-precious metals as well as precious metal catalysts for electroless or chemical plating processes. These patents are included herein by reference. U.S. Pat. Nos. 3,993,491; 3,993,799; 3,993,801; 3,993,848; 3,958,048; 4,048,354; 4,082,899; 4,087,586; 4,131,699; 4,123,832; 4,136,216; 4,150,171; 4,151,311; 4,167,596; 4,180,600; 4,181,759; 4,181,760; 4,220,678; 4,224,178; 3,011,920. Also British Pat. No. 1,426,462 is included by U.S. Pat. No. 3,657,003 hydrous oxide sols have been utilized as a preliminary step or method for rendering nonwettable (hydrophobic) surfaces wettable. In U.S. Pat. No. 3,563,784 a preactivation of synthetic resin has been described. The preactivation step encompasses the use of surfactant solutions. The novelty relates to a composition in which the surfactants are selected from derivatives of acid phosphate esters. In U.S. Pat. No. 3,563,784 the inventor contends that the use of the preferred surfactant composition stems from the resulting decreased surface tension at the substrate interface. In application Ser. No. 061,484 now U.S. Pat. No. 4301190 the use of hydrous oxides, surfactants, and complexing agents are disclosed for usage prior to colloidal non-precious metal catalysts. The prior art has suggested that both positively and negatively charged colloid could be used in the rendering of substrates catalytic for chemical plating.
In U.S. Pat. No. 3,993,848 the use of phenol and derivatives thereof, including miscellaneous aromatics, have been shown as linking agents for Sn/Cu type catalysts. Unfortunately these materials are relatively expensive, requiring large concentrations, and they further impose a major problem in their waste disposal and health hazards. Another limitation encountered is due to excess concentration of these materials (e.g., phenol); it appears to cause a permanent distortion onto the non-conductor substrate (e.g., ABS). In U.S. Pat. No. 3,993,848 the linking agents used are found to be compatible with the Sn/Cu composition, and they appear to increase the adsorption of Sn.sup.+2 ions. Regardless, however, none of the materials disclosed in the above prior art disclose the use of high polymeric polyelectrolytes or flocculants or coagulants.
In some of the references disclosed above, particularly in the electroless plating for printed circuitry (e.g., PTH processing), there appears to be a change in surface charge especially after certain of the etching steps (e.g., ammonium persulfate). Such modification in a surface charge may adversely affect the adsorption and/or absorption of the catalyst (or sensitizer) onto the dielectric substrate or any other substrate and consequently affect its ability for electroless (chemical) plating initiation and as well as the resulting uniformity of plating. Incomplete electroless plating can often lead to skip plating. Such consequences cannot be afforded in many commercial practices. Accordingly, it is highly desirable to provide with a manner by which a simple and inexpensive modification may be adapted compatible with the process and material, thereby insuring increased adsorption of components which lead to the catalytic sites.
At the same time, it is imperative that any new substances employed be inexpensive, compatible with waste-disposal treatment(s) now employed, and not introduce any potential health-hazard problems.